1. Field of the Invention
This invention relates to a reduced-pressure distillation system, which is capable of producing fresh water or clean water of high purity by removing impurities from impure water (e.g., sea water), drainage, and the like, or capable of collecting useful materials from various kinds of discharge liquor containing useful materials, by using a vacuum distillation method or a reduced-pressure distillation method on an energy saving basis.
2. Description of the Prior Art
To obtain fresh water from, for instance, sea water, there are conventionally known various methods, such as a distillation method (i.e., the evaporation method) for heating sea water to distill clean water, a reverse osmosis method for obtaining fresh water by pressurizing sea water to allow the same to pass through a semi-permeable membrane, an electrodialysis for removing salt content from sea water by introducing the water between ion exchange membranes, a freezing method for freezing sea water to obtain fresh water from the thus frozen water, and the like.
In addition, there is also known a vacuum distillation method, alternatively referred to as a reduced-pressure distillation method, in which impure water such as sea water is heated and boiled in an evaporator under vacuum or reduced pressure to generate vapor, followed by cooling the thus generated vapor in a condenser, to thereby collect condensed water. In the vacuum distillation method or the reduced-pressure distillation method, in general, when water is transformed in phase from a liquid phase through a gaseous phase into a liquid phase, a huge amount of thermal energy exchange is generated. To mitigate the thermal energy exchange, the method concerned is characterized by low-temperature distillation by reducing pressure within a container.
Each of the above-mentioned conventional methods, however, requires not only increased facilities costs, but also huge amounts of labor and costs for operational maintenance and control. For example, the reverse osmosis method, which uses a semi-permeable membrane, or the electrodialysis, which uses an ion exchange membrane, each require a membrane with excellent performance for satisfying either pressure resistance or permeability of a specific solution, which renders the conventional method extremely expensive when implemented. In addition, each method inevitably includes complicated procedures such as maintenance, inspection, component exchange during operation of the system.
To cope with the above-mentioned inconveniences, reduced pressure distillation systems having various constructions, have been proposed by applying thereto the vacuum distillation method or the reduced-pressure distillation method, in an attempt to economically and effectively use thermal energy or to operate the system on an energy saving basis or in an efficient manner.
For instance, a vacuum distillation system for distilling and purifying clean water from impure water, such as ground water, agricultural water, industrial water, water for domestic use, has been proposed, for instance, by Japanese Patent Laid-Open Publication No. Hei6-320140. According to the vacuum distillation system, water is supplied to a feed water preheater while an evaporator is filled with water to a predetermined upper limit level, and then the water in the evaporator is heated by activating a refrigerant compressor, followed by cooling a condenser. Further, the interiors of the evaporator and the condenser are kept to low pressure close to vacuum, and then the water is boiled at a relatively low temperature close to a room temperature. Thus, vapor generated in the evaporator passes through an evaporation tube, emits heat in the feed water preheater, and then is introduced into the condenser to be condensed. When the water level in the evaporator drops to a predetermined lower limit level, remaining water in the evaporator is discharged and at the same time condensed purified water in the condenser is collected. According to the vacuum distillation system, energy generated by a solar power, such as solar battery, is employed for energizing an auxiliary electric heater provided for the evaporator, and therefore thermal energy utilization is economically implemented.
Further, a distillation system for distilling useful materials and solvents from a mixed solution containing various materials on a drastic energy saving basis has been proposed, for example, by Japanese Patent Laid-Open Publication No. Hei5-253405. The distillation system is provided with a distiller having a vapor generating chamber and a heat exchanging chamber, and includes solution introducing means for introducing the mixed solution at high temperature into the vapor generating chamber while outside air is prevented from entering the distiller, and drainage discharging means for discharging condensed drainage while outside air is prevented from entering the distiller. In addition, the system includes condensed solution discharging means for discharging the condensed solution containing useful materials into the heat exchanging chamber while outside air is prevented from entering the same, and air excluding means for excluding air within the distiller by blowing air-excluding vapor and interrupting permeation of outside air into the same, the vapor generating chamber and the heat exchanging chamber communicating with each other through a vapor flow path. As a result, distillation is always carried out under a low pressure environment without air remaining therein, to thereby achieve highly efficient distillation by low-pressure evaporation with a small temperature difference over a long time period.
Still further, a reduced-pressure distillation system has been proposed, for example, by Japanese Patent Laid-Open Publication No. Hei9-150001. The system includes a vapor generating block to which is connected a condenser block for carrying out condensation of vapor. Further connected to the condenser block is a storage block for storing a condensed solution. A vacuum pump extends to any or all of the storage block, the vapor generating block, and the condenser block such that pressure therein can be reduced. Further, the storage block has a feed path extending therefrom, for supplying the condensed solution to a supply block. The feed path with a predetermined length, has a first valve arranged thereacross at a location closer to the storage block and a second valve arranged thereacross at a location closer to the supply block and separated from the first valve with a predetermined storage interval. The two valves can be individually opened and closed, and therefore when the condensed solution after completion of condensation is supplied to the supply block, it is not required that reduced pressure in the storage block is released nor distillation work is interrupted. As a result, continuous reduced-pressure distillation can be efficiently achieved.
Although the above proposed reduced-pressure distillation systems have brought about various advantages such as economical and effective use of thermal energy, energy saving, or efficient operation of the systems, they not only have complicated arrangements and facilities, but also require operation and control of a vacuum pump, which unfavorably increase facilities costs.
The present inventors have made extensive and intensive studies and built prototypes in order to obtain a system which is manufactured at reduced facilities costs, as well as small in size, portable, easy in control and operation, and immediately available in an emergency such as disasters. As a result, the present inventors have successively developed a reduced-pressure distillation system which is relatively simple in construction, easy in operation without depending only on driving of a vacuum pump, and therefore can be manufactured and operated at low costs.
The reduced-pressure distillation system proposed here includes an impure water tank, a separating tank, a drainage tank, and a collecting tank, and the impure water tank, the drainage tank, and the collecting tank each has an outside pressure communicating chamber which makes contact with outside pressure such as atmospheric pressure, and a cell which communicates with the outside pressure communicating chamber corresponding thereto and is sealed with respect to outside pressure such as atmospheric pressure during operation of the reduced-pressure distillation system. The separating tank is sealed with respect to outside pressure such as atmospheric pressure and has an evaporator provided therein. The reduced-pressure distillation system is further comprised of feeding means for feeding impure water from the cell of the impure water tank to the evaporator of the separating tank, by using an effective head between a level of impure water stored in the impure water tank and a level of priming supplied to the drainage tank, discharging means for discharging remaining water in the evaporator to the cell of the drainage tank, collecting means for collecting purified water stored in a bottom portion of the separating tank into the cell of the collecting tank, the purified water being obtained by evaporating and condensing the impure water by activation of the evaporator of the separating tank, communicating means communicating with the cells of the impure water tank, the drainage tank, and the collecting tank, respectively, via the separating tank, and evacuation means for carrying out evacuation within the separating tank to keep each of the cells in a pressure-reduced state.
By virtue of the above construction, a reduced-pressure distillation system, which can overcome the aforementioned conventional inconveniences, can be easily obtained.
It is therefore an object of the present invention to provide a reduced-pressure distillation system which is relatively simple in construction, easy in operation without depending only on driving of a vacuum pump, and therefore can be manufactured and operated at low costs.
To attain the above objects, the present invention provides a reduced-pressure distillation system including an impure water tank, a separating tank, a drainage tank, and a collecting tank, the impure water tank, the drainage tank, and the collecting tank each having an outside pressure communicating chamber, which makes contact with outside pressure such as atmospheric pressure, and a cell, which communicates with the outside pressure communicating chamber corresponding thereto and is sealed with respect to the outside pressure during operation of the reduced-pressure distillation system, the separating tank being sealed with respect to the outside pressure and having an evaporator provided therein.
The reduced-pressure distillation system comprising means for feeding impure water from the cell of the impure water tank to the evaporator of the separating tank, by using an effective head between a level of impure water stored in the impure water tank and a level of priming supplied to the drainage tank, means for discharging remaining water in the evaporator to the cell of the drainage tank, means for collecting purified water stored in a bottom portion of the separating tank into the cell of the collecting tank, the purified water being obtained by evaporating the impure water by activation of the evaporator of the separating tank, means for communicating with the cells of the impure water tank, the drainage tank, and the collecting tank, respectively, through the separating tank, and means for carrying out evacuation within the separating tank to keep each of the cells in a pressure-reduced state.
In this case, the outside pressure communicating chamber of the impure water tank may be supplied with the impure water to a predetermined level, the outside pressure communicating chamber of the drainage tank may be supplied with the priming to a predetermined level, the outside pressure communicating chamber of the collecting tank may be supplied with priming consisting of clean water to a predetermined level, the cells of the impure water tank, the drainage tank, and the collecting tank, respectively, may be allowed to communicate with each other, and the separating tank may have its interior evacuated to reduce pressure within each of the cells, whereby levels of the impure water in the cell of the impure water tank, the priming in the cell of the drainage tank, and the priming consisting of the clean water in the cell of the collecting tank can be kept constant with respect to the outside pressure such as the atmospheric pressure.
Furthermore, after keeping constant the levels of the impure water in the cell of the impure water tank, the priming in the cell of the drainage tank, and the priming consisting of the clean water in the cell of the collecting tank, the cells of the impure water tank, the drainage tank, and the collecting tank, respectively, may be prevented from communicating with each other as appropriate, whereby the impure water in the cell of the impure water tank can be fed to the evaporator of the separating tank and the remaining water in the evaporator can be discharged to the cell of the drainage tank, by using the effective head between the level of the impure water stored in the impure water tank and the level of the priming in the drainage tank.
The above and other objects, features and advantages of the invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings.